Gas permeator

ABSTRACT

A method and apparatus for supplying a source of a pollutant gas admixed with an inert gas, wherein the inert gas is passed through a passage defined by a permeator body of a distance sufficient to permit the inert gas to reach thermal equilibrium with the permeator body, and the inert gas is subsequently passed through a centrally disposed opening in the permeator body for admixture with a pollutant gas which has diffused through a gaspermeable container positioned in the opening.

United States Patent 1191 ii I, 1

Lyshkow July 23, 1974 GAS PERMEATOR 3,618,911 9/1969 Martin 73/1 R [75]Inventor: Norman A. Lyshkow, Chicago, Ill. I

Primary Examiner--S. Clement Swisher [73] Assigneez Combustion EquipmentAssociates, 1

' Inc., New York, N.Y. Ki [57] ABSTRACT [22] Filed: Nov. 21, 1972 Amethod and apparatus for supplying a source of a PP 308,540 pollutantgas admixed with an inert gas, wherein the inert gas is passed through apassage defined by a per- [52] U.S. Cl 73/1 R mean body of a distanceSufficient to Permit the 1 [5 H 1m CL L G01 31/00 inert gas to reachthermal equilibrium with the perme- [58] Field Search 48IDIG, 5 atorbody, and the inert gas is subsequently passed through a centrallydisposed opening in the permeator [56] References Cited body foradmixture with a pollutant gas which has diffused through agas-permeable container positioned in UNITED STATES PATENTS g I th:Opening. 3,520,194 7/1970 Adams 7.3/1 R 3,614,855 10/1971 Luik', Jr 73/1R 19 Claims, 5 Drawing Figures i i az '1: 72 F 174 1%, 12 21% 15g 54 f\%/r\ I a g; 35 5g 64 3% Zsii 4% f/ g I, s K t s 1 a2 a 1 a .move mixturesof the pollutant gas and the inert gas from the permeator. As is shownin FIG. 1, the appara- .tus also includes a casing 16 adapted to receivethe permeator body 10.The casing 16 is provided with heating means 18,which are preferably electrical resistance heatersqoperatively connectedto a control box 20 which in turn is operatively connected to a suitablepower source 22. The control box 20 is preferably adjustable by means ofa control 24 to control the power supplied to the heating means 18 andthereby facilitate temperature control. As will be discussed more fullyhereinafter, the heating means 18 are positioned to heat the inert gassupplied to the permeator body.

As is shown in FIG. 1, the casing 16 is formed by a .sleeve 34 which issurrounded by insulating material 36 in which the heating means 18 isembedded;

The inert gas for the system may conveniently be supplied by a tank 26which is'equipped with a valve 28, a pressure reducing valve 30 and,optionally, a pressure gauge 32, all of which are operativelyconnectedto the inlet means l2to supply the inert gas thereto,

The'details of the permeator body and associated casing are more clearlyillustrated in FIG. 2 of the drawing. As can be seen from thisfigure,the permeator body is formed of a flange element 38 integral with abarrel portion 40, with the barrel portion 40 being receivable in thesleeve 34 of the casing 16. The flange portion 38 is provided with anopening 42 adapted to receive the means 12 for supplying the inert gasto the permeator body. As illustrated in FIG. 2, the means 12 ispreferably formed of a nipple portion 44, terminating in a flowconstrictor 46 most preferably in the form of a small diameter needle,facilitating constant flow of the inert gasthrough nipple 44 into theopening 42. The small orifice of the needle'also provides more accuratetemperature control as the inert gas expands and is cooled on passagetherethrough.

Asis also shown in FIG. 2, the barrel portion 40 is provided adjacentthe flange portion 38 with means 48 to secure the permeator body in thesleeve 34. It is generally preferred that the barrel 40 be provided withthread means 48 whereby the upper portion of the barrel 40 is adapted tobe threadedly engaged with the corresponding upper portion of the sleeve34. The wall is also provided with a continuous groove 50 on theperipheralface thereof whereby the groove 50 defines along with theinterior face 52 of the sleeve 34 a pas-.

sage having a high length to cross-sectional area ratio. As isillustrated in FIGS. 2 and 4, the continuous groove 50 can most simplybe formed by providing a continuous thread about the periphery of thebarrel 40 whereby the path defined by the groove 50 and the interface 52of the sleeve 34 is a continuous helix extending over the length of thebarrel.

The barrel also defines an opening 54 between the inlet opening 42 andthe continuous groove 50 whereby the opening 42 communicates with thecontinuous groove 50 to permit gas supplied to the inlet means to bepassed through the needle 46 into the opening 42 and through the opening54 to the continuous groove 50.

As will be appreciated by those skilled in the art, a number ofdifferent types of passages can be defined by the barrel portion 40 ofthe permeator body. It is necessary only, that the passage defined bythe groove 50 be of a sufficient length to permit the inert gas passedtherethrough to reach thermal equilibrium with the barrel portion 40of'the permeator body 10. In other words, the continuous groove 50should provide a high surface area to facilitate heat transfer betweenthe barrel 40 and the inert gas supplied thereto.

The barrel 40 of the permeator body 10 is dimensioned such that thebarrel does not completely extend to the base'56 of the sleeve 34whereby the base 58 of the barrel 40 and the base 56 of the sleeve 34define a small opening 60 communicating with the lower portion of thecontinuous groove 50. In this way, the inert gas which is passed.through the continuous groove 50 exits from the groove 50 into thespace 60.

The permeatorbody 10 also defined a central opening 62 which extendsover the entire length of the barrel40 and the flange 38. At its lowerportion, the central opening communicates with the space 60 at the baseof the barrel whereby inert gas supplied tothe space 60 is passedupwardly through the central opening 62. The central opening 62 isadapted to contain a pollutant gas permeable container or capsule64which can be mounted in the central opening 62 by means of a clip 66.Thus, the inert gas which is caused to pass through the continuousgroove 50 into the opening 60 at the base of the barrel and thenupwardly through the central opening is admixed with the pollutant gaswhich continuously diffuses through the walls of the capsule 64. Thecapsule 64 is preferably formed of a material which is permeable-to thepollutantgas to permit the pollutant gas to diffuse through the walls ofthe capsule 64 at a slow, controlled rate. Such capsules are known intheart and are preferably formed of polymers of tetrafluoroethylene of thetype referred to herein above.

The upper portion 68'of the central opening 62 defined by the flange 38is preferably formed with thread means tothreadingly engage outlet means14 for the removal of pollutant gasadmixed with the inert gas. Asillustrated in FIG. 2, the outlet means 14 can be in the form of arotometer formed of a body portion 70 having a central passage 72 formedof a tapered bore. A flowv indicator such as a ball 74 can be positionedin the tapered bore to indicate the rate of flow of the mixture of theinert gas passing upwardly from the central opening 62 into the centralbore 72. The body portion 70 of the rotometer preferably terminates in anipple 76 for .the attachment of suitable connecting means to pass themixture of the S0 and the inert gas to the instrument to be calibrated.

The flange portion 38 of the permeator body is preferably provided witha shallow cavity 78 adapted to threadedly engage a colorimeter 80 whichin turn is adapted to receive a thermometer 82 or like temperaturemeasuring means to enable the temperature of the permeator body to beascertained.

In an alternative embodiment of the invention, as shown in FIG. 5, theoutlet means 14 can be provided with a T-fitting 84 having a filter 86mounted on one branch thereof which operates to admit to the T- memberambient gas, usually air, which has been puri- GAS PERMEATOR Thisinvention relates to a method and apparatus for use in the calibrationof analytical instruments, and more particularly to an improved methodand apparatus for use in the calibration of gas analytical instruments.

A number of analytical instruments for use in the de tection and/oranalysis of S NO, N0 etc. containing gas streams are well known to thoseskilled in the art. Such instruments can be based on colorimetry asdescribed in my earlier'U.S. Pat. No. 3,617,136. However, as isdescribed'in my copending application Ser. No. 172,133, filed Aug. 16,1971, it has recently been discovered that chemiluminescence can be usedas a basis for analysis of gas streams. Regardless of the mechanism bywhich the analysis is carried out, instruments for use in themeasurement of such gases must, at some point in time, be calibrated,preferably using as a standard a gas stream containing a known quantityof pollutant gas admixed with a gas which is inert to the analyticalsystem of the instrument.

One mode for calibrating analytical instruments involves the use of aclosed tube formed of Teflon (i.e., polymers of tetrafluoroethylene)containing S0 N0 H 8, butane, etc. The gas diffuses throughout theTeflon forming'the tube at a fairly constant, known rate usually of theorder of a few micrograms per'minute. The pollutant gas which diffusesthrough the wall of the tube is admixed'with nitrogen, air which is freefrom the pollutant gas, or any other inert gas, and the resultingmixture is supplied to an analytical instrument as a standard to permitthe instrument to be calibrated. One of the primary difficulties in theuse of such permeable tube in the calibration of analytical instrumentsas described is that the rate of diffusion of the gas through'the Teflonis quite sensitive to temperature, with the rate of diffusion beingsignificantly higher at elevated temperatures. Thus, the accuracy of thecalibration depends in large, measure on the ambient temperature. v v

It has also been found that optimum rates of diffusion of such' gasesthrough the Teflon are achieved when the temperature of the system ismaintained at about 3 l-3 2C. As will be appreciated by those skilled inthe art, it is quite difficult to maintain the permeator system at suchtemperatures, with precise temperature control within normal limits.

,It is accordingly an object of the present invention to provide amethod and apparatus for supplying a known quantity of pollutant gasadmixed with an inert gas for use in the calibration of instruments,using gas permeator which overcomes the foregoing disadvantages andwhich is characterized by more uniform rates of diffusion.

It is another object of the present invention to provide a method andapparatus for supplying a pollutant gas admixed with an inert gas foruse in the calibration of analytical instruments which is completelyportable and can be used under varying ambient temperature conditionsand yet provide a uniform mixture of the pollutant and an inert gas.

It is a more specific object of the present invention to provide amethod and apparatus for supplying a pollutant gas admixed with an inertgas for use in the calibration of instruments in which a gas permeatorcan be maintained in'a state of thermal equilibrium, independent ofambient temperatures, and thereby at a constant temperature.

These and other objects and advantages of the invention will appear morefully hereinafter and, for purposes of illustration but not oflimitation, an embodiment is shown in the accompanying drawing in which:

FIG. 1 is a schematic illustration of apparatus embodying the conceptsof this invention;

FIG. 2 is a detailed view of a permeator employed in the practice ofthis invention;

FIG. 3 is a sectional view of the permeator of FIG. 2 taken along theline 3-3 in FIG. 2;

FIG. 4 is a detailed view of the flow path of the permeator of FIG. 2;

FIG. 5 is a cross-sectional view of an alternative outlet assembly forthe permeator shown in FIGS. 1 to 4.

. The concepts of the present invention reside in a method and apparatusfor providing a supply of a pollutant gas in an inert gas which can beused in the calibration of gas analytical instruments in which an inertgas is passed through a path defined by a permeator body having a highratio of length to cross sectional area to permit the inert gas to reachthermal equilibrium with the permeator body. The inert gas is thenpassed through a passage in the permeator body for contact with acontainer which is permeable to the pollutant gas and which contains thepollutant gas whereby the pollutant gas slowly diffuses through thecontainer for admixture with the inert gas to provide a mixture of thepollutant gas and the inert gas. Because the permeator body is allowedto reach thermal equilibrium, the diffusion of the pollutant gas whichoccurs within the permeator body takes place at a temperaturesubstantially independent of the ambient temperature to provide a sourceof pollutant gas and an inert gas in which the pollutant has is present.in controlled amounts.

The temperature at which the pollutant gas diffuses through thecontainer can be simply controlled by heating the inert gas as it ispassed through the passage whereby the inert gas serves to heat thepermeator body..

As used herein, the term inert gas is intended to refer to and includeany gas which is inert to the analytical system of the instrument to becalibrated. For example, where the instrument is a colorimeter of thetype described in US. Pat. No. 3,617,136, the inert gas should be onewhich is inert to pararosaniline which is reactive with a sulfide ionfor the development of color. A number of inert gases can be used in thepractice of this invention and include nitrogen, helium, argon, air, solong as it is free from even trace amounts of the pollutant gas, as wellas numerous others.

As used herein, the term pollutant gas" is intended to refer to andinclude any gas to which the analytical system of an instrument to becalibrated is sensitive and which is capable of diffusing through a gasin permeable material at a slow, controlled rate. Such gases and gaspermeable materials are themselves well known to the art, and include S0N0 H 8, hydrocarbons such as butane, .etc.

Referring now to the drawings for a more detailed description ofapreferred embodiment of this invention, there is shown in FIG. 1 apermeator system which includes a permeator body 10 having inlet means12 to of gas flow through the analytical instrument is greater than theoutput of the mixture. of the inert gas and the pollutant has from thepermeator of this invention. For example, the calimeter described in myearlier US. Pat. No. 3,617,136, is usually connected to a source of;vacuum to draw a gas to be subjected to analysis rial, and preferably amaterial such as aluminum, steel orthe like. When the material formingthe permeator body is not completely inert to the pollutant gas, it isfrequently desirable to provide theinterior face 90 with a coating 92which is inert to the pollutant gas to prevent or substantially minimizereaction of the pollutant gas, which diffuses from the capsule 64 intothe central opening 62, with the material forming the permeator body 10.The coating 92, as illustrated in FIG. 3 of the drawing, can simply beaplastic film, such'as Teflon or the like.

surrounding the sleeve 34 although it will be understood by thoseskilled in the art that the heating means may be integrated with thesleeve 34 or positioned else where so as to supply heat to the inert gasflowing through the passage defined by the continuous groove v50. Inthis way, the temperature to which the inert gas is heated and hence theequilibrium temperature of the system, can be selected'without regard tothe ambient temperature. a

It will'be'understood that various changes and modifications can be madeinthe details of construction,

operation and use without departing from the spirit of the invention,especially as defined in the following claims.

I claim:

1. A permeator assembly to supply a source of a pollutant gas admixedwith an inert gas comprising a permeator body including a barrel portionhaving an elongate groove about the periphery thereof, a casing adaptedto receive the barrel portion and having an inner face, with the innerface and the casing groove defining a passage having a high ratio oflength to cross sectional area, means to supply an inert gas to saidpassage communicating with said passage, a centrally disposed openingextending through the body, said open- In the operation of the apparatusof this invention, an

inert gas is supplied to the inlet means 12 by the tank 26, and theinert gasflowsthrough the needle44 and the small diameter needle 46 intotheopening 42. Depending somewhat upon the procedure employed, there issome expansion and hence cooling of the inert gas as it emerges from theneedle 46, although such expansion is not necessary-in the practiceofthis invention. The inert gas suppliedto the opening-42 through theneedle 46 is then passed through the opening54 into the continuousgroove 50 wherebythe inert gas in continuously passed through thepassage defined by the groove 50 over the length of the barrel40 toestablish or at least approach thermal equilibrium wi'ththe barrel 40.The inert gas emerges from the passage defined by the groove at the baseof the barrel 40 and is caused to flow into the space 60 and upwardlythrough the central opening 62 where the inert gas is admixed with thepollutant gas which diffuses fromthe capsule 64 into the central opening62. The pollutant gaswhich'has diffused through the capsule 64 is thusswept upwardly throughthe central opening 62 andthrough the outlet means14 for passage to the instrument to be calibrated. As will beappreciated by those skilled in the art, since thermal equilibrium isestablishedbetween the inert gas supplied to the passage defined by thecontinuous groove and the barrel 40of the permeator body, the capsule64, which is displaced in the central opening 62 of the barrel 40, ismaintained at the equilibrium temperature thereby established.Consequently, the pollutant-gas diffuses through the walls forming thecontainer 64 at a constant rate determined by the equilibriumtemperature established.

As is illustrated in FIG. 1, the heating elements 18 are positioned tosupply heat to the inert gas flowing through the cont'inuousgroove 50 tothereby enable the temperature of the inert gas and consequently theequilibrium temperature of the permeator body 10 to be adjusted at thedesired level. As is shown in FIG. 1, the heating elements 18 arepositionedadjacent to and ing communicating with said passage oppositethe means to supply an inert gas and adapted to receive a pollutant gaspermeable container in said opening to diffuse pollutant gas into saidopening for admixture with inert gas supplied through said passage tosaid opening whereby the inert gas supplied to said passage reachesthermal equilibrium with the body and is then passed into said openingto form a mixture of pollutant gas and the inert gas, means to removethe mixture from said opening and means to heat the inert gas suppliedto said passage.

2. An assembly as defined by claim 1 wherein the means to supply aninert gas to said passage includes a I small diameter orifice.

3. An assembly as defined by claim 1 wherein said passage, is a helicalpassage havinga length sufficient to permit the inert gas suppliedthereto to reach thermal equilibrium with the permeator body.

4. An assembly as defined by claim 3 wherein the casing includes asleeve portion adapted to receive the barrel portion of the permeatorbody and temperature insulating means surrounding the sleeve portion.

5. An assembly as defined by claim 4 wherein the heating means arepositioned adjacent to the sleeve portion.

6. An assembly asdefined by claim 1 wherein the central opening containsa thin film of a material to prevent reaction of the pollutant gas withthe material forming the permeator body.

7. An assembly as defined by claim 5 wherein the barrel portion and thecasing define a chamber opposite the means to supply gas to said passagewhereby the central opening communicates with said passage through saidchamber.

8. An assembly as defined by claim '1 wherein the means to remove saidmixture from the central opening includes means to measure the flow rateof said mixture therethrough.

9. An assembly as defined by claim 1 which includes means for measuringthe temperature of the permeator body.

10. An assembly as defined by claim 1 wherein the means to heat theinert gas is adjusted to control the temperature of the permeator body.

11. An assembly as defined in claim 1 wherein the means to remove saidmixture from the central opening includes filter means adapted to admitambient gas to the stream of said mixture removed from the means toremove said mixture from the central opening.

12. A permeator comprising a body including a barrel portion, anelongate groove about the barrel portion to define a passage having ahigh ratio of length to cross sectional area, means to supply an inertgas to said passage communicating with said passage, a centrallydisposed opening extending through the body, said opening communicatingwith said passage opposite the means to supply an inert gas and adaptedto receive a pollutant gas permeable container in said opening todiffuse pollutant gas into said opening for admixture with inert gassupplied through said passage to said opening wherebyv the inert gassupplied to said passage reaches thermal equilibrium with the body andis then passed into said opening to form a mixture of pollutant gas andthe inert gas, and means to remove the mixture from said opening.

13. A permeator as defined in claim 12 wherein the means to supply aninert gas to said passage includes a small diameter orifice.

14. A permeator as defined in claim 12 wherein the permeator bodyincludes a flange portion and a barrel portion, with the passage definedby the periphery of the barrel portion.

15. A permeator as defined in claim 13 which includes a continuousgroove about the periphery of the barrel portion.

16. A permeator as defined in claim 16 wherein the groove is a helicalgroove extending over substantially the entire length of the barrelportion.

17. A permeator as defined by claim 12 wherein the central openingcontains a thin film of a material to prevent reaction of the pollutantgas with the material forming the permeator body.

18. A permeator as defined by claim 12 wherein the means to remove saidmixture from the central opening includes means to measure the flow rateof said mixture therethrough.

19. A permeator as defined by claim 12 wherein the means to remove saidmixture from the central opening includes a filter means adapted toadmit ambient gas to the stream of said mixture removed from the meansto remove said mixture from the central opening.

1. A permeator assembly to supply a source of a pollutant gas admixedwith an inert gas comprising a permeator body including a barrel portionhaving an elongate groove about the periphery thereof, a casing adaptedto receive the barrel portion and having an inner face, with the innerface and the casing groove defining a passage having a high ratio oflength to cross sectional area, means to supply an inert gas to saidpassage communicating with said passage, a centrally disposed openingextending through the body, said opening communicating with said passageopposite the means to supply an inert gas and adapted to receive apollutant gas permeable container in said opening to diffuse pollutantgas into said opening for admixture with inert gas supplied through saidpassage to said opening whereby the inert gas supplied to said passagereaches thermal equilibrium with the body and is then passed into saidopening to form a mixture of pollutant gas and the inert gas, means toremove the mixture from said opening and means to heat the inert gassupplied to said passage.
 2. An assEmbly as defined by claim 1 whereinthe means to supply an inert gas to said passage includes a smalldiameter orifice.
 3. An assembly as defined by claim 1 wherein saidpassage is a helical passage having a length sufficient to permit theinert gas supplied thereto to reach thermal equilibrium with thepermeator body.
 4. An assembly as defined by claim 3 wherein the casingincludes a sleeve portion adapted to receive the barrel portion of thepermeator body and temperature insulating means surrounding the sleeveportion.
 5. An assembly as defined by claim 4 wherein the heating meansare positioned adjacent to the sleeve portion.
 6. An assembly as definedby claim 1 wherein the central opening contains a thin film of amaterial to prevent reaction of the pollutant gas with the materialforming the permeator body.
 7. An assembly as defined by claim 5 whereinthe barrel portion and the casing define a chamber opposite the means tosupply gas to said passage whereby the central opening communicates withsaid passage through said chamber.
 8. An assembly as defined by claim 1wherein the means to remove said mixture from the central openingincludes means to measure the flow rate of said mixture therethrough. 9.An assembly as defined by claim 1 which includes means for measuring thetemperature of the permeator body.
 10. An assembly as defined by claim 1wherein the means to heat the inert gas is adjusted to control thetemperature of the permeator body.
 11. An assembly as defined in claim 1wherein the means to remove said mixture from the central openingincludes filter means adapted to admit ambient gas to the stream of saidmixture removed from the means to remove said mixture from the centralopening.
 12. A permeator comprising a body including a barrel portion,an elongate groove about the barrel portion to define a passage having ahigh ratio of length to cross sectional area, means to supply an inertgas to said passage communicating with said passage, a centrallydisposed opening extending through the body, said opening communicatingwith said passage opposite the means to supply an inert gas and adaptedto receive a pollutant gas permeable container in said opening todiffuse pollutant gas into said opening for admixture with inert gassupplied through said passage to said opening whereby the inert gassupplied to said passage reaches thermal equilibrium with the body andis then passed into said opening to form a mixture of pollutant gas andthe inert gas, and means to remove the mixture from said opening.
 13. Apermeator as defined in claim 12 wherein the means to supply an inertgas to said passage includes a small diameter orifice.
 14. A permeatoras defined in claim 12 wherein the permeator body includes a flangeportion and a barrel portion, with the passage defined by the peripheryof the barrel portion.
 15. A permeator as defined in claim 13 whichincludes a continuous groove about the periphery of the barrel portion.16. A permeator as defined in claim 16 wherein the groove is a helicalgroove extending over substantially the entire length of the barrelportion.
 17. A permeator as defined by claim 12 wherein the centralopening contains a thin film of a material to prevent reaction of thepollutant gas with the material forming the permeator body.
 18. Apermeator as defined by claim 12 wherein the means to remove saidmixture from the central opening includes means to measure the flow rateof said mixture therethrough.
 19. A permeator as defined by claim 12wherein the means to remove said mixture from the central openingincludes a filter means adapted to admit ambient gas to the stream ofsaid mixture removed from the means to remove said mixture from thecentral opening.